1. Technical Field
The present invention relates to an MRI (magnetic resonance imaging) apparatus and a magnetic resonance imaging method which excite nuclear spins of an object magnetically with an RF (radio frequency) signal having the Larmor frequency and reconstruct an image based on NMR (nuclear magnetic resonance) signals generated due to the excitation, and more particularly, to a magnetic resonance imaging apparatus and a magnetic resonance imaging method which make it possible to perform 3D (three-dimensional) cine imaging of a moving part such as a heart under free breath.
2. Description of the Related Art
Magnetic Resonance Imaging is an imaging method which excites nuclear spin of an object set in a static magnetic field with a RF signal having the Larmor frequency magnetically and reconstruct an image based on an MR signal generated due to the excitation.
Conventionally, in the field of MRI, cardiac cine imaging is performed (see, for example, Japanese Patent Application Laid-Open disclosure No. 2007-82753). The MRI cardiac cine imaging uses two-dimensional (2D) imaging in synchronization with an electrocardiogram while a patient holds his/her breath for around 10 seconds. Normally, since a short axis image is obtained so that the entire left ventricle of the heart is covered, it is necessary to repeat imaging with breath-holding around 10 times. Consequently, a technology for segmenting k-space (Fourier space) data to be acquired into some regions (i.e. segmentalization) and sequentially acquiring plural pieces of k-space data each segment during a single breath-holding, that is, a technology for acquiring pieces of data with a segmented sequence is devised.
However, in conventional MRI cardiac cine imaging, there are problems in that image degradation such as image wobble occurs and a slice position is displaced in the case of an image of a patient when it is difficult to hold his/her breath. As a result, there is concern that accuracy of diagnostic, such as cardiac function analysis, decreases. In conventional MRI cardiac cine imaging, a burden for the patient also increases due to repetition of imaging with breath-holding around 10 times.
In addition, in conventional MRI cardiac cine imaging, since it is difficult to improve time resolution and spatial resolution because of constraints in a breath-holding period, three dimensional imaging is thought to be practically unrealistic.
To the contrary, under a parallel imaging method (that is one of high-speed imaging methods devised recently), time resolution and spatial resolution are improved and three-dimensional imaging is tried at the study level.
However, the situation still needs a long breath-holding time of approximately ten-seconds and, moreover, requires a partial sacrifice of resolution.